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After the NIC has been installed, the network cable is attached to the card's port to make the actual physical connection between the computer and the rest of the network.
Run the c02dem01 and c02dem02 videos located in the Demos folder on the CD accompanying this book to view a demonstration of how to install a network interface card (NIC).
Figure 2.24 A sample NIC
The role of the NIC is to:
Data moves through a computer along paths called buses. These are actually several data paths placed side by side. Because the paths are side by side (parallel), data can move along them in lateral groups instead of in a single (serial) data stream.
Older buses, such as those used in the original IBM personal computer, were known as 8-bit buses because they could move data 8 bits at a time. The IBM PC/AT computer used a 16-bit bus, which means it could move data 16 bits at a time. Computers manufactured today use 32-bit buses. When data travels on a computer's bus, it is said to be traveling in parallel because the 32 bits are moving along side by side. Think of a 32-bit bus as a 32-lane highway with 32 cars moving side by side (moving in parallel), each carrying one bit of data.
On the network cable, however, data must travel in a single stream of bits. When data travels on a network cable it is said to be traveling as a serial transmission because one bit follows another. In other words, the cable is a one-lane highway, and the data always travels in one direction. The computer is either sending or receiving data, but never both at the same time.
The NIC takes data that is traveling in parallel as a group and restructures it so that it will flow through the 1-bit-serial path of the network cable. Figure 2.25 shows a server converting parallel data to serial data on the network. This is accomplished through the translation of the computer's digital signals into electrical or optical signals that can travel on the network's cables. The component responsible for this is the transceiver (transmitter/receiver).
Figure 2.25 Parallel data stream converted to a serial data stream
In addition to transforming data, the NIC also has to advertise its own location, or address, to the rest of the network to distinguish it from all the other cards on the network.
A committee of the Institute of Electrical and Electronics Engineers (IEEE) assigns blocks of addresses to each NIC manufacturer. The manufacturers hardwire these addresses into chips on the card by a process known as "burning" the address into the card. With this process, each NIC—and therefore each computer—has a unique address on a network.
The NIC also participates in several other functions in sequence as it takes data from the computer and gets it ready for the network cable:
Each NIC signals to the other indicating its own parameters and accepting
or adjusting to the other card's parameters. After all the communication
details have been determined, the two cards begin to send and receive data.
Settings on older NICs are made by means of software, jumpers, or a combination of both; see the NIC product documentation for the appropriate software or jumper settings. Many newer NICs use Plug and Play (PnP) technology; consequently, older cards that require setting options manually are becoming obsolete. (Plug and Play is discussed in more detail later in this lesson.)
Figure 2.26 Older NIC with DIP switches
Interrupt request lines are built into the computer's internal hardware and are assigned different levels of priority so that the microprocessor can determine the relative importance of incoming service requests.
When the NIC sends a request to the computer, it uses an interrupt—an electronic signal sent to the computer's CPU. Each device in the computer must use a different interrupt request line. The interrupt line is specified when the device is configured. For examples, see Table 2.5 that follows.
In most cases, IRQ3 or IRQ5 can be used for the NIC, as we will see later in this chapter. IRQ5 is the recommended setting if it is available, and it is the default for most systems. Use a system diagnostic tool to determine which IRQs are already being used.
If neither IRQ3 nor IRQ5 is available, refer to the following table for alternative values to use. The IRQs listed here as available usually can be used for a NIC. If the computer does not have the hardware device listed for a specific IRQ, that IRQ should be available for use.
Table 2.5 Standard IRQ Settings
|IRQ||Computer with an 80486 processor (or higher)|
|2(9)||EGA/VGA (enhanced graphics adapter/video graphics adapter)|
|3||Available (unless used for second serial port [COM2, COM4] or bus mouse)|
|5||Available (unless used for second parallel port [LPT2] or sound card)|
|7||Parallel port (LPT1)|
|15||Available (unless used for secondary hard-disk controller)|
Each hardware device in a system must have a different base I/O port number. The port numbers, in hexadecimal format (the system that uses 16 rather than 10 as the basis for its numbering) in the following table, are usually available to assign to a NIC unless they are already in use. Those with a device listed next to them are addresses commonly used for the devices. Check the computer documentation to determine which addresses are already in use.
Table 2.6 Base I/O Port Settings
|200 to 20F||Game port||300 to 30F||NIC|
|210 to 21F||310 to 31F||NIC|
|220 to 22F||320 to 32F||Hard-disk controller (for PS/2 Model 30)|
|230 to 23F||Bus mouse||330 to 33F|
|240 to 24F||340 to 34F|
|250 to 25F||350 to 35F|
|260 to 26F||360 to 36F|
|270 to 27F||LPT3||370 to 37F||LPT2|
|280 to 28F||380 to 38F|
|290 to 29F||390 to 39F|
|2A0 to 2AF||3A0 to 3AF|
|2B0 to 2BF||3B0 to 3BF||LPT1|
|2C0 to 2CF||3C0 to 3CF||EGA/VGA|
|2D0 to 2DF||3D0 to 3DF||CGA/MCGA (also EGA/VGA, in color video modes)|
|2E0 to 2EF||3E0 to 3EF|
|2F0 to 2FF||COM2||3F0 to 3FF||Floppy-disk controller; COM1|
A data frame is a packet of information transmitted as a unit on a network. Often, the base memory address for a NIC is D8000. (For some NICs, the final "0" is dropped from the base memory address—for example, D8000 would become D800.) When configuring a NIC, you must select a base memory address that is not already being used by another device.
NICs that do not use system RAM do not have a setting for the base memory address. Some NICs contain a setting that allows you to specify the amount of memory to be set aside for storing data frames. For example, for some cards you can specify either 16 KB or 32 KB of memory. Specifying more memory provides better network performance but leaves less memory available for other uses.
Making the choice on the card is usually done with jumpers. Jumpers are small connectors that tie two pins together to determine which circuits the card will use.
Figure 2.27 Network interface card showing external
and on-board transceivers
Industry Standard Architecture (ISA)
ISA is the architecture used in the IBM PC, XT, and AT computers, as well as in all their clones. It allows various adapters to be added to the system by means of plug-in cards that are inserted in expansion slots. ISA was expanded from an 8-bit path to a 16-bit path in 1984 when IBM introduced the IBM PC/AT computer. ISA refers to the expansion slot itself (an 8-bit slot or a 16-bit slot). The 8-bit slots are shorter than the 16-bit slots that actually consist of two slots, one behind the other. An 8-bit card could fit into a 16-bit slot, but a 16-bit card could not fit into an 8-bit slot.
ISA was the standard personal-computer architecture until Compaq and several other companies developed the EISA bus.
Extended Industry Standard Architecture (EISA)
This is the bus standard introduced in 1988 by a consortium of nine computer-industry companies: AST Research, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse Technology, and Zenith.
EISA offers a 32-bit data path and maintains compatibility with ISA, while providing for additional features introduced by IBM in its Micro Channel Architecture bus.
Micro Channel Architecture
IBM introduced this standard in 1988 at the time it released its PS/2 computer. Micro Channel Architecture is electrically and physically incompatible with the ISA bus. Unlike the ISA bus, the Micro Channel functions as either a 16-bit or a 32-bit bus and can be driven independently by multiple bus master processors.
Peripheral Component Interconnect (PCI)
This is a 32-bit local bus used in most Pentium computers and in the Apple Power Macintosh computers. The current PCI bus architecture meets most of the requirements for providing Plug and Play functionality. Plug and Play is both a design philosophy and a set of personal computer architecture specifications. The goal of Plug and Play is to enable changes to be made to a personal-computer configuration without any intervention by the user.
Figure 2.28 ISA, EISA, Micro Channel, and PCI
network interface cards
As discussed in the previous lesson, each type of cable has different physical characteristics that the NIC must accommodate. Each card is built to accept at least one type of cable. Coaxial, twisted-pair, and fiber-optic are the most common cable types.
Some NICs have more than one interface connector. For example, it is not uncommon for a NIC to have a thinnet, thicknet, and twisted-pair connector.
If a card has more than one interface connector and does not have built-in interface detection, you should make a selection by setting jumpers on the card itself or by using a software-selectable option. Consult the NIC documentation for information on how to properly configure the card. Three examples of typical connectors found on NICs are shown in the following three illustrations.
A thinnet network connection uses a coaxial BNC connector as shown in Figure 2.29.
Figure 2.29 Thinnet network connection for a coaxial BNC connector
A thicknet network connection uses a 15-pin attachment unit interface (AUI) cable to connect the 15-pin (DB-15) connector on the back of the NIC to an external transceiver. As discussed earlier in Lesson 1, the external transceiver uses a vampire tap to connect to the thicknet cable. Figure 2.30 shows a 15-pin AUI connection.
Figure 2.30 Thicknet network connection for a 15-pin AUI
Be careful not to confuse a joystick port with an AUI external transceiver port; they look alike, but some joystick pins carry 5 volts DC, which can be harmful to network hardware as well as to the computer. You need to be familiar with the specific hardware configuration in order to determine whether the connector is for a NIC or a joystick. Similarly, be careful not to confuse 25-pin SCSI ports with parallel printer ports. Some older SCSI devices communicated through the same kind of DB-25 connector as these parallel ports, but neither device will function when plugged into the wrong connector.
Figure 2.31 RJ-45 connector
After identifying the physical requirements of the NIC—the computer bus, the type of connector the card needs, and the type of network in which it will operate—it is necessary to consider several other factors that affect the capabilities of the card.
Although all NICs conform to certain minimum standards and specifications, some cards feature enhancements that greatly improve server, client, and overall network performance.
You can speed up the movement of data through the card by adding the following enhancements:
Wireless NICs often come with many features. These include:
Usually, these NICs are used to communicate with a component called a wireless concentrator that acts as a transceiver to send and receive signals.
A concentrator is a communications device that combines signals from multiple sources, such as terminals on a network, into one or more signals before sending them to their destination.
However, because computers normally start from either a floppy or a hard disk, there has to be another source for the software that initially starts (boots) the computer and connects it to a network. In these environments, the NIC can be equipped with a special chip called a remote-boot PROM (programmable read-only memory) that contains the hardwired code that starts the computer and connects the user to the network.
With remote-boot PROMs, diskless workstations can join the network when
Most experienced network engineers check cabling first because experience has taught them that the majority of network problems can be found in the cabling.
The most common network adapter problems are interrupt conflicts and transceiver settings. The following questions will help you determine if the NIC is the source of your problem.
You have a 20-user, thinnet, coaxial bus network that has been in use for about a year. Three new client computers are going to be added to the network. Your vendor installed the new computers over the weekend, but when you came in Monday morning, nobody could access the server.
The answers identify some of the potential causes of the problem, but the list is not exhaustive. Even if the answers you have written down are not listed, they might still be correct.